The present invention relates to a pneumatic tire and a method of making the same, and more particularly to an improvement relating to the carcass by which the road noise is reduced.
Recently, passenger cars strongly require less noise generation and quietness during vehicle operation. Therefore, it is necessary to decrease the noise generated from tires and the transmission of the noise from the tire to the inside of the car. Road noise is a type of noise heard in a car. Road noise has a peak in the low frequency range of around 250 Hz, which is almost the same as the resonance frequency of passenger cars. During running, the tread portion vibrates due to the roughness of the road surfaces, and the vibrations are transmitted through a suspension mechanism and amplified to about 250 Hz. Therefore, the inside of the car tends to resonate or vibrate which is very uncomfortable for the driver. This is especially noticeable in a radial tire whose tread portion is reinforced with a stiff belt.
It is therefore necessary for reducing the road noise to decrease the sound level of a peak with a frequency of about 250 Hz.
In order to reduce the road noise, the tread rubber hardness is decreased to decrease the tread rigidity, or the tread rubber thickness is increased to provide a cushion effect against the shock which the tread receives, or a foam rubber material is adhered to the inner surface of the tire as a vibration damper layer.
In such conventional countermeasure, however, desirable results can not be obtained. If the tread rigidity is decreased, the cornering force is decreased and the steering stability deteriorates. If the damper layer is used, the ride comfort is impaired, and the tire loses its weight balance about its rotational axis. Further, the manufacturing method increases in the number of the steps and the manufacturing cost increases.